1. Field of the Invention
The invention relates generally to devices and methods for controlling and removing the buildup of mineral scales and the like upon subsurface safety valves.
2. Description of the Related Art
Surface-controlled, subsurface safety valves (“SCSSV's”) are typically used in production string arrangements to quickly close off the production flowbore in the event of an emergency, such as a blowout. A usual form for an SCSSV is a flapper-type valve that includes a flapper member that is pivotally movable between open and closed positions within the flowbore. The flapper member is actuated between the open and closed positions by a flow tube that is axially movable within the flowbore.
After being placed into a wellbore, mineral scale typically forms and builds up on all portions of the production tubing string that are exposed to wellbore fluids. Portions of the flowbore that have a pressure drop are particularly vulnerable to scale buildup. Scale and other buildup forming on and around the flow tube of the SCSSV can make it difficult to move the flow tube axially and thereby prevent proper operation of the SCSSV. Of particular concern is the interior surface of the flowbore within the valve housing that is located above the flow tube, as scale buildup in that location can prevent the flow tube from moving axially and prevent the valve from closing.
Wireline brushes can be used to try to clean the scale buildup from the flow tube and surrounding valve housing. However, this is costly as it necessitates stopping production operations to run the brush in and then conduct the cleaning.